Could this be used to fill a plaster of Paris mold?

Not that I'm aware of, it doesn't really say on the package but it does sit up very fast and is very durable. Sorry but that's the best I can answer your question.

Could this be used to hold an 8x8 supporting a substantial weight?

I had to replace a 4x4 post for my mailbox and used this 2K Post Back Fill. I already had a deep hole in the cement, so this stuff fills up the gaps beautifully all around and keep the post solidly planted. I'm not sure about 8x8, weight is not the issue here but you would need a "solid" hole like in my case to hold to post, then this foam would then fill up any gaps. Good luck.

Can this be used to form the deck list foundation where the 8x8 post then sits on top held by a bracket anchored in the foundation?

No, Fast 2K can only be used for installing posts that are sunk into the ground. It cannot be used as a foundation material nor can any brackets be anchored into it.

Would this be good to use for posts for a horse fence strong and sturdy?

Yes, also sets up quick and should be good for a horse fence.

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Weatherables Fast 2k Fence Post Backfill

Product ID: 75636303

Details

Brand
H.B. Fuller
Colour
No Color
Item form
Foam
Material
Adhesive
Special feature
Waterproof

⚡Sets posts in 15 mins

💧Waterproof & hydrophobic

🪶Lightweight 32.8 oz bag

MX$5561

Duties & taxes included

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Sold byAmazon MexicoDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

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Description

🚀 Set it, forget it, and flex your fence game!

RAPID POST SETTING - Forget hours of curing—posts lock in place within 15 minutes for instant progress.
EFFORTLESS HANDLING - Lightweight, compact bags replace heavy concrete—save your back and skip the mess.
WATERPROOF PROTECTION - Hydrophobic formula prevents rot, rust, and water damage—extend your post’s lifespan.
ALL SEASON RELIABILITY - Works flawlessly even in winter—no water or hardware needed for year-round projects.
PROFESSIONAL GRADE STRENGTH - Utilizes utility pole tech with expanding composite for superior hold and durability.

Weatherables Fast 2k Fence Post Backfill is a lightweight, expanding composite foam that sets fence posts securely in just 15 minutes without water or mixing mess. Using professional utility pole technology, it offers waterproof, rot-resistant protection and works in all seasons, making it the smart, fast, and durable alternative to traditional concrete.

Specifications

ASIN	B00LAFUC34
Best Sellers Rank	572,562 in DIY & Tools ( See Top 100 in DIY & Tools ) 2,494 in Posts
Brand	H.B. Fuller
Colour	No Color
Compatible Material	Metal, Plastic, Wood
Container Type	Bag
Customer Reviews	4.3 4.3 out of 5 stars (1,671)
Global Trade Identification Number	00669602000322
Included Components	Multitool Accessory
Item Form	Foam
Item Package Quantity	1
Item Type Name	Fast 2K 26OZ Back Fill
Item Volume	32.8 Fluid Ounces
Item Weight	2.2 Pounds
Manufacturer	H.B. Fuller
Manufacturer Part Number	254-20-S
Material	Adhesive, Sealant
Model Number	250
Number of Packs	1
Number of Pieces	1
Other Special Features of the Product	Waterproof
UPC	713976908484 669602000322
Unit Count	1.0 count
Water Resistance Level	Waterproof

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MX$5561

Duties & taxes included

In stock

Sold byAmazon MexicoDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

Buyer Protection · Full refund if your order doesn't arrive as described.

Desertcart purchases this item on your behalf and handles shipping, customs, and support to Mexico.

Secure transaction

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TrustScore 4.5 | 7,300+ reviews

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